1. Field of the Invention
This invention relates generally to methods and apparatuses for the treatment of waste materials, and more particularly, the present invention relates to an improved method and apparatus for plasma gasification of hazardous and non-hazardous waste materials by utilizing at least one graphite DC electrode in a refractory lined reactor vessel.
2. Description of the Prior Art
As is generally well known, the daily generation of solid waste material, such as Municipal Solid Waster (MSW) and its disposal thereof, have become major problems in the past few decades as more and more waste is being generated by residential and commercial facilities. The use of landfill sites for the disposal of such MSW does not solve the problems due to all of the existing sites becoming full, coupled with the fact that they contaminate groundwater and adjacent properties. As a result, there are substantial public concerns relative to land space allocation and environmental damage.
In view of this, there have been developed heretofore certain Energy From Waste (EFW) technologies that can provide more efficient and less costly disposal systems by creating energy as a by-product of the destruction process. The most widely known type of EFW facility is incineration in various forms. However, these incinerator EFW systems tend to cause a great deal of air pollution. Consequently, EFW systems based on the gasification process have been developed in the alternative that can produce a lower emission of all environmental contaminants.
For example, in U.S. Pat. No. 5,280,757 to Carter et al., issued on Jan. 25, 1994, there is disclosed a process for treating municipal solid waste that includes feeding, compressing, and forcing a stream of solid waste into the bottom of a reactor vessel heated with a plasma torch.
Further, in U.S. Pat. No. 5,534,659 to Springer et al., issued on Jul. 9, 1996, there is taught a method and apparatus for treating hazardous and non-hazardous waste materials consisting of inorganic and organic components. A plasma arc torch is used to heat a waste processing chamber to a sufficient temperature for converting the organic components of the waste material to a gas and for converting the inorganic components of the waste material to a molten material.
In addition, there is shown in U.S. Pat. No. 6,380,507 to Wayne F. Childs, issued on Apr. 30, 2002, a method and apparatus for processing waste material to produce energy and other reusable materials therefrom which utilizes a plasma arc furnace having at least one hollow electrode. The hollow electrode is projected into a molten pool of material to create the plasma arc to heat the furnace. Waste material is fed through the hollow electrode into the molten pool to ionize and disassociate the waste material.
However, plasma torch-type furnaces are not economical due to the fact that they have to be water cooled, using metallic electrodes that also need to be water cooled. Thus, the plasma torch-type furnaces are inefficient since a substantial amount of the energy that is generated is wasted in the cooling water. Further, the plasma torch arc may radiate in a manner to cause heavy impingement on the refractory-lined walls of the furnace, thereby shortening its useful life. In addition, the plasma torch-type furnaces suffer from the disadvantage of insufficient heating of the bottom of the surface. While a furnace that uses a hollow electrode operates adequately for finely ground or shredded waste materials, it does not perform efficiently with waste products that have not been processed.
Accordingly, it would be desirable to provide an improved method and apparatus for plasma gasification of hazardous and non-hazardous waste materials that is relatively simple and inexpensive in design, construction, and operation. It would also be expedient that the apparatus for plasma gasification of hazardous and non-hazardous waste materials utilizes at least one graphite DC electrode in a refractory-lined reactor vessel so as to allow for a more uniform temperature to be maintained throughout the entire depth of the reactor vessel.
None of the prior art discussed above disclosed an apparatus for plasma gasification of hazardous and non-hazardous waste materials like that of the present invention which includes at least one graphite DC electrode disposed in a molten bath in a refractory-lined reactor vessel. The present invention represents a significant improvement over the aforementioned '757, '659, and '507 prior art patents discussed above.